Body is thin, tapering anteriorly and posteriorly.
Prostomium conical, with two relative large black or dark brown eyes on the posterior half of the prostomium. Prostomium with two dorso-lateral lobes, more or less fused with the first achaetous segment. Anterior two achaetous segments dorsally fused. One pair of long thick palps on the last achaetous segment. Achaetous segments are much longer than the chaetigers. Filamentous gills start at first chaetiger or last achaetous segment.
Chaetae capillary, bent, of different size and thickness.
From 17-21th notopodium and from first neuropodium also bidentate, subdistally finely winged hooks, with a maximum of 7-8 in middle neuropodia (C. alata-chaetae).
Up to 12 mm for 110 segments.
In alcohol brownish to grey.
American west coast from Canada to southern Chile, Southwest Atlantic between Ireland and South Africa, Mediterranean, English Channel and southern North Sea.